植物种间相互作用对物种的生存至关重要。对于入侵植物而言, 更强的种间竞争能力是其成功入侵的重要机制。然而, 环境条件的变化可能会改变种间关系并影响植物入侵的最终结果。该研究主要探索当今严重的环境问题之一——酸雨对中国入侵植物豚草(Ambrosia artemisiifolia)和伴生本地种鬼针草(Bidens bipinnata)种间相互作用的影响, 进一步了解环境扰动对生物入侵的影响。该研究于2021年3月在北京师范大学室外条件下对豚草和鬼针草开展de Wit替代竞争实验, 并施加不同浓度的酸雨模拟溶液(pH = 3、4、5、7), 记录植株在第24、34、45天的株高以及生长季结束时的株高和地上生物量, 通过计算相对邻株效应指数(RNE)并绘制取代系列图表来评估两者的竞争关系。主要结果如下: 单一种植时, 中浓度酸雨(pH = 4)促进了豚草和鬼针草的早期生长, 而高浓度酸雨(pH = 3)显著抑制了两者的早期生长, 但不影响生长季结束时的株高。混合种植时, 高浓度酸雨(pH = 3)显著降低了豚草在第34、45天时的株高, 但在生长季结束时对豚草无影响, 而鬼针草在生长季结束时株高显著降低。鬼针草相对豚草的RNE在任何酸浓度下都不显著。而豚草相对鬼针草的RNE在无酸雨条件下显著, 酸雨处理时在鬼针草比例较低时显著。取代系列实验图表显示, 低浓度酸雨(pH = 5)增加了在低豚草比例下的鬼针草的竞争优势, 而高浓度酸雨增强了豚草的竞争优势。该研究表明酸雨显著影响了豚草和鬼针草的生长及种间竞争关系, 高浓度酸雨增加了入侵植物豚草的竞争优势。

Aims The interspecific interactions between plants are vital for species survival. For biological invaders, stronger competitive ability allows them to invade successfully when appearing with indigenous species, which is considered as an important mechanism underlying successful invasion. However, environmental changes may alter interspecific interactions, thus impacting invasion consequences. In this study, we aimed to explore the effect of acid rain, which is a seriously environmental problem worldwide, on the interactions between a Chinese invader common ragweed (Ambrosia artemisiifolia) and its accompanying indigenous forb (Bidens bipinnata) to further explore the role of an environmental disturbance in biological invasions.

Methods In March 2021, we performed a de Wit replacement competitive experiment with A. artemisiifolia and B. bipinnata at the campus of Beijing Normal University; meanwhile we also simulated acid rain through providing different concentrations of solutions (pH = 3, 4, 5, 7). Plant height after 24, 34, 45 days, final plant height, and aboveground biomass were determined for each individual plant. Relative neighbor effect (RNE) and replacement diagrams were used to estimate interspecific competition.

Important findings When the two species were planted separately, the medium level of an acid solution (pH = 4) promoted their early growth, and the high level of an acid solution (pH = 3) significantly inhibited their early growth but did not affect the final plant height. When grown together, the ragweed showed a decrease in plant height in the presence of the high level of an acid solution (pH = 3) after 34 and 45 days, but this negative effect disappeared at harvest. The plant height of bidens applied with the high level of an acid solution (pH = 3) decreased significantly at harvest compared with the control treatment. The RNE of bidens on ragweed was not significant under all the treatments, while the RNE of ragweed on bidens was significant without acid application or under the condition of acid treatments at a lower proportion of bidens. Replacement diagrams showed that the bidens had an advantage over ragweed when applied with the low level of an acid solution (pH = 5) at higher proportions, and the ragweed had an enhanced advantage over bidens when applied with the high level of an acid solution (pH = 3). Our study suggests that acid rain might affect the growth of ragweed and bidens as well as their interactions, and acid rain with low pH may boost the competitive advantage of invasive ragweed.